Moon wrasse (Thalassoma lunare)

Moon Wrasse

The  moon wrasse,  Thalassoma lunare, is a species of  wrasse  native to the  Indian Ocean  and the western  Pacific Ocean. It is an inhabitant of  coral reefs  and surrounding areas at depths from 1 to 20  m (3.3 to 65.6  ft). Moon wrasses are carnivorous and tend to prey on fish eggs and small sea-floor dwelling invertebrates. This species can reach 45  cm (18  in)in total length. It is of minor importance to local  commercial fisheries  and can also be found in the  aquarium  trade.


The juvenile is blue on the lower half of its body, with a black spot in the middle of the dorsal fin and a black blotch on the caudal fin base. As it matures, the spot turns into a yellow crescent, hence the name. The body is green, with prominently marked scales. Coloration of the head ranges from blue to magenta, with a broken  checkerboard  pattern.

Moon wrasses are active fish, said to be moving all day long. They are also territorial, nipping, chasing, and otherwise harassing fish that get in their way.

Being  diurnal, wrasses have strong vision, although they also have a decent sense of smell. At night, they rest in niches often under rocks or other such structures. If needed, a moon wrasse may dig out a space under a rock by repeatedly swimming through it until it fits without struggle.

They are  protogynous  hermaphrodites, all starting off as females and changing to males, a process which, for the moon wrasse, takes only 10 days. Some moon wrasses live in groups consisted of a dominant male, and a “harem” of about a dozen other wrasses, some female and some male. The alpha male is more brightly colored, and at every low tide hour, changes from green to blue, and goes into a show of attacking and nipping all the other wrasses. This is his way of showing his dominance to the rest of the males and keeping the females in check. During breeding season and before high tide, the alpha male turns completely blue, gathers up every single female, and the spawning frenzy begins.

Moon wrasses may live up to a decade in captivity, although this is shorter in the wild. They are popular fish in the aquarium trade, due to their hardiness, bright colors, and engaging behavior. They are renowned for their ability to tolerate spikes in  nitrate, and eat  bristle worms, a fish keeper’s pest.


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